Our objective is to increase our understanding of cellular mechanisms involved in implantation of the blastocyst. Implantation in the Rhesus monkey is being examined using both transmission and scanning electron microscope methods following perfusion fixation. Stages to be examined include pre-implantation embryos and uterus, initial adhesion of blastocyst to uterus, penetration of uterine epithelium, and early post-implantation stages including formation of placental villi. In addition, studies of the surface membrane components of trophoblast and uterine luminal epithelium at the site of implantation in non-primate laboratory animals are continuing, using scanning electron microscopy and transmission electron microscopy. Autoradiographic analysis of incorporation of amino acids and sugars in uterine glands will be completed.